There is an urgent need for an effective chemical-free control measure for crown gall. Crown gall is a major disease of many perennial crops. It is especially a problem in long-lived woody crops such as roses, where galls on rose bushes render plants unsalable. In the case of woody fruit and nut producing crops such as walnut, grapes, pears and apples, galled trees and vines are less productive. Losses of 10 to 30% have been reported and control with chemicals has both an environmental cost and a significant business costs, estimated at more than a $1000 per acre for roses alone. Rose and other nursery crop growers currently work under an EPA Critical Exemption for the use of such chemicals. This exemption could be lifted at anytime.